net/ena: switch to pci_alloc_irq_vectors

BugLink: http://bugs.launchpad.net/bugs/1701575
Remove the deprecated pci_enable_msix API in favour of its successor.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit da6f4cf58e403628de026f06b608005beb8995ba)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>